ISSN : 0974 - 7443
Volume 9 Issue 1
chemical technology An Indian Journal Full Paper CTAIJ 9(1) 2014 [27-31]
Characterization of Bangladesh sand for possible high-tech applications Marzia Hoque Tania, A.S.W.Kurny, Fahmida Gulshan* Dept. of Materials and Metallurgical Engineering, Bangladesh University of Engineering and Technology, Dhaka, (BANGLADESH) E-mail :
[email protected]
ABSTRACT Sand samples from 5 deposits in Bangladesh was characterised on the basis of parameters that include composition, size, density, sphericity, moisture content, material composition and crystallinity for possible use in the production of silicon for high-tech applications. The results have been presented and discussed. 2014 Trade Science Inc. - INDIA
INTRODUCTION
tions including the production of solar grade silicon.
Bangladesh is undertaking ambitious programmes MATERIALS AND METHODS to increase the use of off-grid, renewable energy technologies[1]. A photovoltaic system probably repreStudy area sents the shortest route to an affordable electricity opSamples of silica sand were collected from 5 diftion for remote and difficult to access villages. The domi[2] nant material used in PV cells is silicon . About 95% ferent locations in Bangladesh (TABLE 1). of the current solar cell module market is based on siliTABLE 1 : Location of the study area con as raw material[3]. Silicon, the main constituent of Location Latitude Longitude silica does not occur in free state, but silicon compounds Sample Sub(E) District (N) are abundantly available and constitute about 28% of district the earth’s crust. Dalia Jaldhaka Nilphamari 26.15 89.03 In nature, silica occurs in different forms such as Kuakata Kalapara Patuakhali 21.82 90.12 [4] quartz, sandstone, quartzite and silica sand . High pu- Patgram Patgram Lalmonirhat 26.35 89.02 rity silica sand for high-tech applications is currently Bipinganj Durgapur Netrokona 25.11 90.67 sourced from a few locations situated in USA, UK, Sylhet Jaintiapur Sylhet 25.13 92.12 Germany, Belgium, France, and Brazil[4-6]. In Bangladesh 94773 tons of glass sand has been exploited during Experimental The samples were characterised on the basis of pa1975-93[7]. Geological Survey Bangladesh has identified new deposits of silica sand. However, systematic rameters that include composition, size, density, sphecharacterization of sands of these deposits is yet to be ricity, moisture content, material composition and crysundertaken. This work aims at evaluating silica of some tallinity. The mineralogical composition of the samples deposits in Bangladesh for possible high-tech applica- was determined by x-ray fluorescence analysis. Par-
Characterization of Bangladesh sand for possible high-tech applications
28
CTAIJ, 9(1) 2014
Full Paper ticle size distribution was analysed by Taylor sieve analysis. The bulk density was determined by a calibrated pycnometer. The sphericity of the particles in the samples was determined by using the following formula Sphericity= (a+ b+ c)/ 3: a where the longest diameter is a, diameter perpendicular to the longest diameter is b and diameter intersecting the other two at 45° is c (Figure 1).
fraction patterns were recorded. Thermogavitimetric analysis (TGA) was performed to determine the thermal effects - to trace the loss of combined water and/or to observe if any polymorphic transformation took place. The samples were heated to 1000°C at a rate of 20°C/ min. Thermogravimetric analysis was performed again on the same sand samples heated for one hour at 580°C. RESULT AND DISCUSSION Optical microscopy
Figure 1: Sphericity Measurement
To determine the organic matter content, a certain quantity of oven dried sample was placed on an empty, clean and dry porcelain dish and the weight of the dish and sand specimen was determined. The dish was then placed in a muffle furnace and the temperature of the furnace was gradually increased to 440°C and the specimen was left there over-night. Then the dish was removed, allowed to cool to room temperature and the mass of the dish containing burned sand was determined. The difference in weight gave the organic matter content[8]. The phases present in the samples were identified by x-ray diffraction analysis. The samples were finely ground in an agate mortar before the x-ray dif-
The colour, size and shape of the samples were observed under a stereo-microscope (Figure 2 (a-e)). Then the prepared grain slides were observed under a polarizing microscope (Figure 2(f-j)). Polarizing microscopic images indicated high silica content in the Bipinganj sand. An analysis was performed on all samples with the Michel-Levy interference colour chart[9,10]. The presence of feldspar, iron oxide etc. could also be found in the samples. The results of analysis for Si02 are given in TABLE 2. Material composition X-ray fluorescence analysis of the samples is shown in TABLE 3. It can be seen that the SiO2 content are in the range 65-97%. Results obtained through Michel-Levy inter-
Figure 2 : Stereo-microscopic view of (a) Dalia, (b) Kuakata, (c) Patgram, (d) Bipinganj and (e) Sylhet sand and Polarizing microscopic view of (f) Dalia, (g) Kuakata (crossed polarized), (h) Patgram, (i) Bipinganj (crossed polarized) and (j) Sylhet (plane-polarized)
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Full Paper TABLE 2 : Polarizing Microscope data
Sample location
from TABLE 2 presence of phosphorus as P2O5 can be seen.
% of Si02
Dalia
74.82
Grain size
Kuakata
60.5
Patgram
81.18
Bipinganj
94.10
Sylhet
85.49
The results of sieve analysis (TABLE 4) show that more than 85% of Dalia sands are sized within 212 ìm to 600 ìm. The result shows among all five samples Kuakata sand size is most tightly distributed, around 84% is 106 ìm (>75 ìm). Sylhet sand is also quite
TABLE 3 : Sand Sample Composition (XRF Analysis)
Content (Weight %) SiO2 Na2O MgO Al2O3 P2O5 K2O CaO TiO2 Cr2O3 MnO Fe2O3
Dalia 75.06 1.74 1.16 11.94 0.08 3.15 1.13 0.29 0.58 0.08 4.62
Kuakata 65.23 1.56 2.42 11.55 0.57 1.95 6.20 1.13 0.43 0.20 8.52
ference colour chart (TABLE 2) are in good agreement with the results of x-ray fluorescence analysis (TABLE 3). The analyses show that Bipinganj sand has the highest Si02 content (~97%), whereas Kuakata sand has the lowest Si02 content. It contains around 35% of oxides other than silica, including oxides of iron, aluminum, titanium etc. All samples, except the Bipinganj sand, contained Al2O3 in good quantity. Aluminum, calcium and other metal oxides are undesirable in the silica[11] for high tech applications. The most troublesome elements in the use of the silica for the manufacturing of the photovoltaic cells are boron and the phosphorus[12];
Patgram 75.52 1.80 1.21 12.05 0.06 3.26 0.99 0.27 0.49 0.07 4.12
Bipinganj 97.04 0.05 0.05 0.90 0.01 0.04 0.06 0.19 0.43 0.01 1.12
Sylhet 86.85 0.41 0.31 5.62 0.05 2.07 0.38 0.26 0.69 0.04 3.17
tightly distributed. Around 93% of sylhet sand is sized within 425 ìm to 106 ìm, where 60% of Sylhet sand is sized around 212 ìm (>106 ìm). Figure 3 shows non-uniformity in Dalia, Patgram and Bipinganj sand. If equal size distribution becomes necessary for subsequent processing, these three sand samples will require grinding and/or screening. Bulk density The bulk density of all five samples measured at a room temperature of 20 °C is given in TABLE 5. The result shows Kuakata sand sample has the highest density (2.9 g/cc). The reason for this can be
TABLE 4 : Sieve analysis of sand samples
Mesh Size
Size (ìm)
6 3.35E03 12 1.70E03 30 600 40 425 70 212 140 106 200 75 270 53 Pan Pan AFS Grain Fineness No
Dalia 0.83 3.88 29.88 26.44 29.32 7.30 0.86 0.97 0.52 40.78
Kuakata Nil 0.03 0.01 0.01 0.66 84.46 12.34 2.47 0.02 107.06
% of Sand retained Patgram Bipinganj 1.55 0.88 4.53 3.30 32.75 23.08 25.47 15.32 27.88 29.93 5.60 20.03 0.85 3.25 0.70 2.13 0.67 2.09 38.61 59.46
Sylhet 0.42 0.65 3.44 11.53 59.96 21.50 1.26 0.65 0.60 60.53
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Figure 3 : Particle Size Distribution
The x-ray diffraction patterns showed the presence of large amount of quartz-form of silica in the samples (Figure 4). The result shows samples of Bipinganj and Sylhet contain only quartz. The other three samples also
TABLE 5 : Sample Characterization
Sample Dalia Kuakata Patgram Bipinganj Sylhet
Moisture % 0.49 0.98 0.59 0.58 0.78
Density (g/cc) 2.58 2.90 2.57 2.60 2.69
understood from XRF result (TABLE 2), which shows presence of heavier materials in Kuakata sand. The density of the pure SiO2 is in the range 2-2.3 g/cc and the density of pure quartz is 2.65 g/cc; cristobalite and tridymite have much lower densities because these two have comparatively open structures, whereas the atoms in quartz are more loosely packed[13]. The collected samples show slight deviation from the ideal value.
Organic Material % 0.39 0.63 0.50 0.07 0.55
Sphericity 0.83 0.838 0.84 0.859 0.86
showed traces of phases other than silica. The unidentified peaks may be of feldspars’ or other silicate minerals.
Organic matter The percentage of organic content is listed in TABLE 5. The result shows presence of negligible amount of organic matter in all five samples. The highest content of only 0.07% was found in Bipinganj sand; this minor percentage may be from the dry leaves’ particle mixed in the sand. These results are in good agreement with the results of thermal analysis. Roundness and sphericity Though the five samples were collected from different locations the sphericity measurement shows (TABLE 5) similar values. This indicates that the samples have gone through similar amount of erosion. Moisture TABLE 5 shows that all five samples contain negligible amount of moisture, which reduce the necessity of drying the sand prior beneficiation step. The result shows Dalia sand sample contains least amount of moisture whereas Kuakata sand contains the highest. It was obchemical technology An Indian Journal
Figure 4 : X-Ray Diffraction patterns: (a) Dalia, (b) Kuakata, (c) Patgram, (d) Bipinganj and (e) Sylhet sand
Dependence on temperature All five of the samples show peaks at ~ 573°C indicating a transformation. It is well-known that áquartz transforms to â-quartz at that temperature[14]. In the patterns of Sylhet sand, there were two additional peaks at 450°C and 810°C (Figure 5). These peaks could be due to loss of combined water and/or carbon dioxide, change of polymorphic form, recombination of the elements into a different compound. To clearly identify the reason, the sample was heated at 580°C for an hour and DTA was performed again. This time other than peak at ~573°C no additional peaks were found (Figure 6), which confirms that there is only one change in polymorphic form of the samples under
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Full Paper REFERENCES
Figure 5 : Differential thermal analysis
Figure 6 : Thermogravimetric analysis of (a) Sylhet, (b) Bipinganj, (c) Dalia, (d) Patgram and (e) Kuakata sand
investigation (i.e. from á-quartz to â-quartz). CONCLUSIONS This study shows that Bipinganj sand with about 97% quartz, low moisture content, negligible clay binder and least organic matter is the most serious contender for use for the production of silicon for high-tech application. Sylhet, Patgram and Dalia sands, with certain limitations, also have good potential. Kuakata sand has the least silica content. Studies may be undertaken to further upgrade the samples from Bipinganj, Sylhet, Dalia and Patgram.
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